Project Summary Consequences of progressions in substance use and high risk sexual behavior (HRSB) from adolescence through adulthood are detrimental to individuals and costly to society. To date, much research has focused on increasing our understanding of the etiological and maintaining mechanisms of health risk behaviors during adolescence as well as on the development of evidence based preventative interventions targeting these behaviors. Affiliation with deviant peers, family conflict and lack of parental monitoring have all been identified as targetable risk factors for engaging in health risk behaviors, such as HRSB and substance use, in adolescents.Additionally, we have learned a substantial amount about the developmental trajectories and the co-occurrence of health-risk behaviors, at least during adolescence. However, there are a number of gaps in the literature to be addressed. First, the vast majority of research on these two categories of risky behavior approaches each as separate phenomena, despite substantial evidence that substance use and HRSB share etiology and often co-occur. Second, adolescence receives the majority of attention in the study of problem behavior and much less is known about the trajectory of these behaviors into young adulthood, despite the fact that many health risk behaviors, including substance use disorders, have been shown to be more prevalent in young adulthood than in any other developmental period, including adolescence. Third, many existing studies are limited by small sample sizes, a cross-sectional or short-term longitudinal design, or data from a single reporter, making it difficult to detect effects, determine causation, and measure constructs of interest in a valid and accurate way. Thus, more longitudinal research is needed to document the concurrent trajectories of HRSB and substance use. Such research needs to 1) capture the developmental processes underlying risk behaviors that is unique to young adulthood, 2) examine the relative contributions of multiple peer and family risk factors simultaneously and 3) utilize strong measurement techniques to accurately assess constructs of interest. Through secondary data analysis of a large, multi-method, multi-informant longitudinal dataset, the proposed study aims to address a number of shortcomings in the current literature and answer new questions that have practical and theoretical implications for etiology, maintenance and prevention of HRSB and substance use during young adulthood. Aim 1 will examine the factor structure and concurrent trajectories of HRSB and substance use during young adulthood (age 23-30). Aim 2 will explore the factor structure and influence of association with deviant peers, parental monitoring, and family conflict in adolescence on trajectories of HRSB and substance use during young adulthood. Aim 3 will test association with deviant peers, parental monitoring, and family conflict as potential mediators of the effect of a preventative intervention on trajectories of HRSB and substance use during young adulthood.